This invention pertains to a copper based powder mixture for infiltrating a porous mass of ferrous material whereby a clean, erosion-free infiltrated iron compact can be produced.
The strength of iron powder compacts can be increased by infiltrating the compacted powder iron matrix with a metal having a melting point lower than that of iron. The lower melting infiltrant is placed on the surface of the iron compact in the amount sufficient to fill the voids in the compacted iron matirx upon heating to a temperature sufficient to melt the infiltrant. The resulting mass is often heated to a temperature sufficient to sinter the iron as well as melting the infiltrant and such a process is known in the art as "sintration" or sintrating. The resulting infiltrated compact has a final strength greater than that of a non-infiltrated iron powder compact. Infiltrating processes for iron base compacts ordinarily provide copper infiltrating powder, iron or other metal to reduce erosion of the iron compact, and a refractory parting compound to facilitate removal of residue remaining after infiltration. The infiltrating composition is usually preformed into a slug which is then placed on the iron compact for filtrating.
Various infiltrating compositions suggested in the past, however, very often leave a residue which adheres to the infiltrated compact. The residue often sticks to the infiltrated part and must be chipped or ground off after the infiltration is completed. U.S. Pat. No. 2,401,221 suggests a simple copper mixture containing a minor amount of iron powder although removal of excess iron residue remains a problem. Erosion of the infiltrated compact is a further problem due to iron from the compacted iron matrix being dissolved by copper. Hardening compounds or refractories such as magnesium oxide or titanium dioxide are incorporated into the infiltrating composition for the purpose of releasing a residue left behind from the infiltrating composition. For example, U.S. Pat. No. 3,307,924 suggests an infiltrate composition preformed into a slug that leaves a residue which shrinks and warps into a husk-like residue which may be easily removed from the infiltrated part; whereas, U.S. Pat. No. 3,619,170 suggests the inclusion of minor amounts of iron-chromium alloy within the infiltrating composition which substantially reduces the tendency of such residues to adhere and/or erode the infiltrated metal compact whereby the remaining residue can be removed by a gravitational force. U.S. Pat. No. 3,652,261 suggests a copper pre-alloy containing as essential alloying elements along with iron manganese, aluminum and nickel. Prealloyed copper materials however, exhibit low compressability and low green strength. Also, pre-alloyed materials do not contain refractory metal oxides which aid in the separation of the residue from the infiltrated iron part. Alloyed materials rely upon in-situ formation of refractory or metal oxide during the infiltrating process, but such materials are very sensitive to the furnace atmosphere, the dew point of the furnace atmosphere, and the infiltrating temperature since the amount of oxide formed is sensitive to these parameters.
It now has been found that a copper infiltrating powder containing certain minor amounts of admixed powders of iron, copper-manganese alloy, stainless steel, and aluminum, improve the infiltrated iron compact by avoiding residue adhesion, migration or soiling, improving efficiency, and avoiding erosion of the compact. The resulting infiltrated compact exhibits improved strength and better hardness as well as controlled density and dimensional changes.